Plasma processes occur, for example, in plasma processing and coating devices. A great number of different plasma processing devices are known, for example, PVD, PECVD, etching or even gas laser excitation. One form of such a device is also known in general terms as a sputtering system on account of the sputtering process used. In particular in the case of dc sputtering installations, flash-overs, where a current seeks an electrically conductive path in the plasma, are a frequent occurrence. Such flash-overs occur relatively frequently, in particular during what is known as reactive coating of a substrate. The reason for this is the fact that in addition to the substrate itself, parts of the sputtering system, such as the inner wall of the process chamber, are coated with electrically non-conducting or only poorly electrically conducting materials, which then charge up to a breakdown voltage. To avoid undue damage to the sputtering systems, the supply of current of a plasma dc voltage supply is switched off or briefly interrupted as soon as possible during the occurrence of a flash-over, or a voltage across the plasma chamber is short-circuited or its polarity is reversed. In order to be able to initiate the above-mentioned measures at all, devices for arc discharge detection (arc detection) and also for suppressing or extinguishing the arc discharges (arcs), are in many cases an integral part of the plasma current supply or plasma dc voltage supply, i.e. the plasma power supply.
In the first instance, it is important that arc discharges or arcs are reliably detected. An arc discharge can be detected, for example, by a voltage dip or voltage drop or by a current rise at the output of the plasma dc voltage supply. In other words, an arc discharge detection (arc detection) can be implemented by monitoring at least one suitable characteristic value of the plasma process, such as one of the above-mentioned electrical characteristic values.
In addition to what are called “hard arcs”, which may lead to damage of the sputtering system and to defects in a substrate to be machined, in particular also what are commonly termed “short arcs” are known (arcs that are relatively strongly defined, but in contrast to hard arcs are self-extinguishing) and what are commonly termed “micro-arcs” (hereafter also referred to as micro arc discharges or micro arcs). Depending on the setting of the threshold for arc discharge detection, such micro arc discharges, when they extinguish themselves again, are generally not detected at all by the known methods and devices. However, it is known that such micro arc discharges can become amplified and can then lead to a more serious short arc or hard arc.
To preclude this happening, it is known, for example, from EP 0 692 138 B1, to reverse the polarity of the voltage supply periodically for a predefinable short time to discharge any charges in the plasma chamber. This is also referred to as DC pulsed operation. Compared with a continuous plasma process, arcing is often clearly reduced with this operation, but the coating or ablation rate is likewise reduced.